28-Noroleanane-derived spirocyclic triterpenoids and iridoid glucosides from the roots of Phlomoides umbrosa (Turcz.) Kamelin & Makhm with their cytotoxic effects

Four undescribed 23,24-O-isopropylidene-19(18 → 17)-abeo-28-noroleanane-derived spirocyclic triterpenoids and an undescribed 28-noroleanane-derived spirocyclic triterpenoid, together with five known 28-noroleanane-derived spirocyclic triterpenoids, were isolated and identified. In addition, three undescribed iridoid glucosides and four known ones were also identified. All the isolates were identified using spectroscopic techniques, and the absolute configurations of 28-noroleanane-derived spirocyclic triterpenoids were determined by CD method for the first time. Additionally, the alkaline hydrolysis method and HPLC analysis were applied to confirm the moieties of the iridoid glucosides. The fraction and isolates were evaluated for cytotoxic activity on cervical cancer (Hela), human promyelocytic leukemia (HL-60), and breast cancer (MCF-7) cell lines. Among them, phlomisu E possessed an aldehyde group showed the most potent cytotoxic effect with IC₅₀ value less than 10 μM.